Today, onium salts have a wide variety of uses, for example as textile auxiliaries, disinfectants and as phase-transfer catalysts.
Quaternary ammonium salts in particular are used in the textile industry as textile softeners, viscose additives, auxiliaries for wet fastness or, in dyeing, as levelling agents or retarders and as stripping agents and discharge agents. Furthermore, textiles are rendered antiseptic and antistatic by applying quaternary ammonium salts. In the cosmetics industry and in medicine, the bactericidal, germicidal and fungicidal properties of quaternary ammonium salts are also used for cosmetics and disinfectants. In addition to being used as flotation auxiliaries (for example in the production of potassium salts), as wetting agents in the production of crude petroleum and as emulsifiers in polymerisation reactions, onium salts in general, and quaternary ammonium salts and phosphonium salts in particular, are used as highly active phase-transfer catalysts. A large number of organic reactions, such as substitution, elimination, oxidation, reduction, Wittig and Aldol reactions may be considerably accelerated by means of phase-transfer catalysis. The rapid high molecular weight synthesis in polycondensations in the interphase process is to be mentioned in particular, in which case valuable thermo-plastic plastics materials, such as polycarbonates and polyesters are obtained.
However, the bactericidal effect of quaternary ammonium and phosphonium compounds contained in waste waters from production and/or use of those onium compounds have a deliterious effect on biological clarifying plants normally used to clean water waters. There is then the danger that the bacterial cultures of the clarifying plant may be severely affected or killed. If a decomposition of quaternary ammonium compounds is to be expected at all in a biological clarifying plant, then it is only a very slow and incomplete decomposition. However, decomposition is required by law. Thus, it would be desirable to remove onium compounds from the waste water before being sluiced into the clarifying plant.